I read some where, possibly here, that BTZS tubes shorten the time for developing compared to Trays. I thought I might make a tube and try it. 1) Is there a rule of thumb for reducing the time in tubes? (assume PMK averages 12-14mins in tray, what is change in tube time?) 2) What is amount of developer needed for 4x5? 1/2 tube, 3/4 tube? more less? 3) Is contrast increased/decreased by the constant spinning in a waterbath? 4) Would PMK require a change of developer midway due to oxidation? or would I just use more developer? thanks in advance!